Its unmanned, but it does have a manned capability, so obviously these would be shorter duration missions. Also adding a widget to an existing sat, perhaps years after its launch, and returning some other widget that was in originally seems like a useful idea.
X-37B has no provisions for crew of any kind, nor is the Atlas V launch vehicle crew-rated, and the way the X-37B is processed and encapsulated is not consonant with astronaut safety procedures and requirements. A scaled up derivative has been proposed by Boeing as a future crewed vehicle, presumably launched on the SLS, but no work has been done to design or test such a vehicle, and no RFP or contract has been issued.
“Adding a widget to an existing sat” is not really feasible unless the satellite has been designed to accept other modules or components in service. While on-orbit servicing of satellites, most notably the Hubble Space Telescope, has been performed in the past, it has often required improvised procedures and using purpose designed fixtures. The desire to make satellites modular to support on-orbit servicing or salvage and reuse has been widely discussed and conceptualized, including “TinkerToy/Lego” type satellites with highly modular construction and even with the ability to self-assemble or reconfigure, but to date there isn’t anything in orbit that is purpose-designed to be serviceable or repairable, and a highly maneuverable vehicle like the X-37B would be useful to support that, but I strongly doubt it is performing any actual servicing or augmenting operations on existing satellites.
Stranger
Thread hijack - Would it have been cheaper and more effective to have an unmanned descent vehicle for returning satellites to Earth? My off-the-cuff idea is to have both the crewed and unmanned vehicles rendezvous with the satt, and have the crew do the tricky work of loading the satt into the unmanned return vehicle. Crewed vehicle can be smaller because it does not have to return much cargo, and the cargo return vehicle is much simpler because it does not have to be human rated. Just a thought, 40 years too late.
Yes and yes. But the merit in returning a satellite back to Earth for servicing is pretty questionable to begin with. Except for the giant telecom birds, space observatories, and surveillance satellites, the cost of the launch represents a substantial portion of the end-to-end cost of the satellite mission, and the potential for damage in handling and transporting the satellite makes retrieval and redeployment a questionable proposition at best. Future satellites are likely to skew toward smaller and cheaper to build, making even less sense for retrieval. It would make more sense to design satellites so that the structure can be salvageable for future use, since the cost of lifting mass is the most prohibitive toward building large space structures, or so that age-sensitive elements such as batteries, flywheels, and solar panels could be easily serviced.
The retrieval and return mission requirement was mostly about giving the STS a reason to exist rather than a genuine scientific or commercial need. In fact, much of the requirements that drove the design of the Space Shuttle system were about giving it the appearance of utility rather than actually useful functionality. There was an alternate proposal by the then Chrysler Aerospace which proposed a giant capsule-shaped reusable single-stage-to-orbit vessel with a modular base aerospike propulsion system and base reentry profile. Whether it would have worked or not is unknown, but independent review of the system by the Aerospace Corporation found that the basic concept was feasible.
Stranger
I’m just impressed that the landing gear tires (and to a lesser extent, the landing gear shock struts) are still viable for a successful landing, after nearly 2 years of being cold-soaked in a hard vacuum.
Who IS Kim Jong-Un’s hair stylist?
If the tires are anything like those of the space shuttle, then they’re inflated to 300+ psi; it doesn’t make much difference whether the ambient pressure is 14.7 psi or zero, as it means the gauge pressure (the differential across the tire material) will only differ by about 5%. Fill them with nitrogen, and use special tires with an extra-thick layer of butyl rubber (this is the layer of a pneumatic tire that has deliberately low permeability to air/nitrogen), and they should last just fine.
Gas struts? Same situation, except the leak path is considerably smaller than a tire carcass. If we can build gas struts that work for a decade on your car’s trunk/hood, then building one that lasts a couple of years in space shouldn’t be a problem.
I never thought of this, but I immediately flashed on the O-rings in the Challenger.
Nope, not part of the weapons.
The aircraft contains a tank with a couple gallons of hydrazine. It powers a device called the Emergency Power Unit (EPU). The F-16 is, obviously, a single engine aircraft. If the hydraulic pump quits, the airplane, due to negative static stability, swaps ends and shatters in a second to two tops. Likewise if the electrical generator quits the battery lasts just a few minutes before it dies and the controls freeze and the airplane swaps ends and …
The engine itself quitting fails both those things at once. The EPU provides limited redundancy against those failures.
If any of those three things happen, the hydrazine (kept under (IIRC 2000psi) nitrogen pressure) is vented into a catalyst bed. Which decomposes the hydrazine into gaseous nitrogen and ammonia at extreme temps & pressures with a multi-thousand to 1 volume expansion. Which hot high pressure gasses are then vented through a turbine and overboard. The turbine turns an electrical generator and hydraulic pump to keep the aircraft flyable to a forced landing or bailout as the situation develops over the next few minutes. The EPU goes from sitting there to full 50-ish horsepower output in a small fraction of a second. And is about the size & weight of a gallon milk jug; super dense power to weight & power to volume. Just what’s needed in a small high performance bleeding edge machine.
Because the hydrazine tank is actively pressurized every second of every day of the aircraft’s life, a leak won’t be a drip; it’ll be a violent spray mist of hydrazine.
The good news is the system has proven very, very reliable in thousands of aircraft times tens of thousands of days. Leaks and unexpected EPU firings are very, very rare.
In the very early prototype days this wasn’t so true. Leaks or inappropriate EPU firings were sorta common during the prototype era. So hydrazine precautions were real big in the early days. By my era (mid-late 1980s) the situation had calmed a bunch. It was a well understood and well respected hazard. But one known to be 99.9999% latent.
The EPU exhaust port is on the right side of the engine inlet just behind the nose gear. There’s a nearby safety pin & flag that you *really *want to make sure is installed before servicing the aircraft.
I had the same immediate thought. Struts & tires are one of the less reliable systems on aircraft beasue they spend so much time sitting idle in hostile surroundings. The X-37B is (so far) the limit case of that.
Inquiring minds wish to know…
Thank you for your fascinating explanation LSLGuy. I was most interested in the bit I quoted - forewarned is forearmed!
I know you used to fly the F-16, so I appreciate your insight.
The orbital space environment–with the high thermal cycling in virtual vacuum, no convective cooling, energetic ionized gas, and unfiltered ultraviolet and ionizing radiation–is particularly harsh and damaging to many materials that are robust on Earth, and JHBoom is quite right to be impressed that the landing systems (and the reentry thermal protection systems) are functional and reliable during reentry, and on the landing for the inaugural OTV-1 flight, one of the tires did rupture and damage the underside of the vehicle during landing. The study of materials suitable for long term use in space is an extensive discipline within materials science and a large body of literature, and as it happens the AIAA Journal of Spacecraft and Rockets devoted an entire issue last year (Vol. 53, Issue 6, November 2016, “Special Issue on Materials in a Space Environment”) to the topic of materials in the space environment containing twenty-five papers on topics varying from mechanical effects on exposed Teflon to thermal and electrical properties of materials exposed to space radiation and rarified ionized atmosphere.
It frequently amazes me how dismissive people often are about materials and compatibility issues in non-terrestrial environments as if we can just build a protective dome for a base on the Moon or Mars out of concrete, steel, and unanodized aluminum and expect it to last for decades with minimal servicing, or we can build flexible seals and tread in a pressure suit that would withstand an expedition-class hike across the surface of Mars even though the solid aluminum wheels of the Curiosity rover started showing wear through and breaking grousers from the abrasive Martian regolith within a few kilometers. Anyone who has owned an ocean-going boat or worked on marine equipment knows how harsh that environment can be, and the sea is positively benign (in some respects) compared to the unfiltered radiation and thermal vacuum environment of space. Dealing with material robustness and compatibility issues in the space environment is a significant challenge for developing a robust industrial space architecture, and particularly one to support long term human habitation where a systemic material failure has the potential for catastrophe.
Stranger
If only it were that simple.
I’ve worked in aviation for over 23 years, both military and civilian. The simple fact that daily tire pressure checks are a requirement on every aircraft I’ve ever worked on that has wheeled landing gear, is one of many indicators that the aerospace environment is a little more demanding than the automotive environment. Especially when the emphasis is on the “space” portion of aerospace.
“D&R?”
Regards,
Leo
“Duck & Run”
Ahh. I thought it was a signature/sign-off I wasn’t hep too. Hence my regards.